Skeletal Muscle Contraction

Question 0

Epimysium

Answer 0

Connective tissue surrounding the entire muscle

Question 1

What is the hierarchical organization of skeletal muscle

Answer 1

Epimysium->Muscle->Perimysium->Fascicle->Endomysium->Sarcolemma->Myofiber->Myofibril->Myofilament (sarcomere)

Question 2

Muscle components

Answer 2

Made of multiple fascicles

Question 3

Perimysium

Answer 3

Connective tissue covering individual fascicles

Question 4

Fascicle

Answer 4

A bundle of myofibers

Question 5

Endomysium

Answer 5

Connective tissue lining each myofiber

Question 6

Sarcolemma

Answer 6

Cell membrane of muscle fiber (aka, plasmalemma)

Question 7

Myofiber

Answer 7

Individual, multinucleated muscle cell (aka, muscle cell)

Question 8

Myofibril

Answer 8

A chain of sarcomeres within a muscle fiber/muscle cell

Question 9

Myofilament

Answer 9

Actin and myosin filaments that make up a sarcomere

Question 10

What do T-tubules do and where are they found?

Answer 10

Found in the sarcolemma, close to the cisternae of the SR… They transport the action potential through the muscle cell

Question 11

What are the bands of a sarcomere and what do they contain

Answer 11

Z-disc: at ends of sarcomere, anchors actin filaments I-band: composed of only actin, width changes H-band: composed of only myosin, width changes A-band: composed of entire myosin filament and a portion of actin filament, width does not change M-line: formed when H-band brings together actin filaments forming the M-line

Question 12

Explain the process of muscle contraction

Answer 12

1)Action potential reaches end of axon opening voltage-gated channels releasing ach into synaptic cleft, which open ligand-gated Na+ channels sarcolemma, generating action potential in sarcolemma 2)Action potential in sarcolemma travels down T-tubules to the DHP which interacts with ryanodine-receptors to release Ca++ from SR into cytosol 3)Ca++ binds to troponin which moves tropomyosin off of myosin binding sites on actin and myosin filaments walk down actin filaments 4)Ca++ is pumped back into SR by active transport and also sequestered by calsequestrin

Question 13

What are DHP receptors

Answer 13

Voltage-gated channels on T-tubules of sarcolemma that cause a change in ryanodine receptors allowing Ca++ to leave SR and enter cytoplasm

Question 14

What are Ryanodine receptors and SERCA

Answer 14

Ryanodine receptors (RyRs) are on the cisternae of the SR and respond to a conformational change in the DHP receptors allowing Ca++ to flow into the cytoplasm… SERCA= ATPase pump that pumps Ca++ back into the SR

Question 15

Calsequestrin

Answer 15

Helps maintain the proper Ca++ concentration in the SR and cytoplasm by binding to Ca++ and bringing it back in the SR after contraction

Question 16

When is there no tension on the muscle

Answer 16

When the sarcomere is fully relaxed and there is no interaction b/w myosin and actin

Question 17

When does tension on the muscle begin and reach its max

Answer 17

When the actin and myosin begin interacting, tension begins…tension reaches its max when the actin filaments come together and the M-line is formed…after that, tension begins to decrease again

Question 18

Where is ATP used during muscle contraction

Answer 18

Mainly during sliding filament mechanism…pumping Ca++ back into the SR and Na+ and K+ ions out and into the cell to repolarize the cell

Question 19

How much ATP is available for contraction…

Answer 19

1-2 seconds worth

Question 20

How does the phosphocreatine energy system work

Answer 20

It reconstitutes the ATP and provides enough energy for 5-8 seconds of contraction

Question 21

How does glycolysis contribute to muscle contraction

Answer 21

Allows for ~1 minute of contraction, but causes build up of lactic acid

Question 22

What is the main energy source for longterm muscle contraction

Answer 22

Oxidative Phosphorylation…accounts for ~95%

Question 23

Isometric Contraction

Answer 23

Causes increase in tension, but not muscle length

Question 24

Isotonic Contraction

Answer 24

Causes increase in tension and change in length… 2 types: Concentric & Eccentric

Question 25

Concentric Muscle Contraction

Answer 25

Occurs when the muscle shortens

Question 26

Eccentric Muscle Contraction

Answer 26

Occurs when the muscle lengthens

Question 27

Fast Twitch Fibers

Answer 27

Contract rapidly but have low endurance… Few mitochondria & myoglobin, larger amount of ATPase… Primarily uses anaerobic respiration… White in color

Question 28

Slow Twitch Fibers

Answer 28

Contract slower but have high endurance… More mitochondria & myoglobin, less ATPase… Primarily uses aerobic respiration… Reddish in color

Question 29

Answer 29

A) DHP

B) Ca++

C) Terminal Cisternae

D) SR

E) Ca++ Release Channel (RyRs)

F) Ca++

G) RyRs

H) Calsequestrin

I) Ca++

Question 30

Answer 30

1) Myofibrils
2) Z line
3) Triad of the reticulum
4) A band
5) I band
6) T-tubule
7) SR
8) T-tubule
9) Terminal Cisternae
10) Sarcolemma